Conventionally, radiation images captured using radiation as represented by an X-ray image are widely used for the purpose of diagnosis of disease, etc. Such medical radiation images were conventionally captured using screen/film. However, lately, digitalization of radiation images is realized, and for example, a CR (Computed Radiography) apparatus is widely used in which after radiation transmitted through an object is accumulated on a photostimulable phosphor sheet formed with a photostimulable phosphor layer, the photostimulable phosphor sheet is scanned with a laser beam and with this, photoelectric conversion is performed on the photostimulable luminescence emitted from the photostimulable phosphor sheet to obtain the image data.
In the radiation image capturing, a cassette (For example, see Patent Document 1-3. Hereinafter referred to as a “CR cassette”.) with a storage medium such as a screen film, photostimulable phosphor sheet, etc. stored inside is used. The CR cassette is designed and manufactured according to size of the JIS (Japanese Industrial Standards) standard of the cassette for screen/film so that the CR cassette can be continuously used in an existing bucky device. In other words, the compatibility of the size of the cassette is maintained to achieve effective utilization of the facilities and digitalization of the image data.
Lately, as a method to obtain a medical radiation image, a FPD (Flat Panel Detector) is known as a detector to detect emitted radiation and to obtain digital image data (For example, see Patent Document 4.), and further a portable capturing apparatus (Portable FPD. Hereinafter, referred to as FPD cassette.) storing an FPD in a housing is put into practical use (For example, see Patent Document 5.).
In such FPD cassette, for example, a scintillator to convert the emitted radiation to light and a photoelectric conversion element such as a photodiode to convert the light to an electric signal are stored in a box (housing) and an electric signal accumulated in the photoelectric conversion element is read out to obtain image data.
Also, lately, a radiation image capturing system (For example, see Patent Document 6.) is known in which an environment with high work efficiency and ease of operation for a radiological technologist, doctor, etc. (Hereinafter referred to as an operator.) can be obtained where X-ray capturing apparatuses of different types with different detection sections are mixed and an image quality at a certain level can be obtained. Also, a radiation image capturing system (For example, see Patent Document 7.) is known to capture a moving image using a FPD cassette to capture a dynamic state of breathing of a chest of a human body.    Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2005-121783    Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2005-114944    Patent Document 3: Japanese Patent Application Laid-Open Publication No. 2002-156717    Patent Document 4: Japanese Patent Application Laid-Open Publication No. 9-73144    Patent Document 5: Japanese Patent Application Laid-Open Publication No. 2006-058124    Patent Document 6: Japanese Patent Application Laid-Open Publication No. 2001-149358    Patent Document 7: Japanese Patent Application Laid-Open Publication No. 2003-290184